These two acronyms plague email setting control panels everywhere, so let’s take a deeper look at them. POP stands for Post Office Protocol. It’s useful because, like a post office, you can pop in, grab all of your mail, and then leave. You don’t need to stay connected, and aside from leaving a copy on the server, it’s a pretty cut-and-dry procedure. If you don’t leave a copy on the server, it doesn’t require much space or bandwidth either. You can use POP to grab mail from several different inboxes on several different email servers and consolidate them on one.
It has its drawbacks, though. POP is a unidirectional protocol; information travels one way. Once you download the email to a client, it’s up to the client to sort through its different statuses and so on. That’s fine if you only ever access mail from one place. Nowadays, though, it’s common to get email access from your phone’s client, the web interface when you’re away somewhere, and a client when you’re at home. It’d be tedious to sort through all of that info over several devices, assuming you’ve even kept a copy of each email on the server to begin with.
IMAP’s a bit smarter about things. While POP can be considered to be very “client-oriented,” the Internet Message Access Protocol was designed to work in a different way: it’s “server-oriented,” and bi-directional. Clients have a two-way communication with their servers. All messages are kept on the server so multiple clients can access them. When you check an email on your phone, it’s marked as read and during the next interaction with the server, that status is sent back so all other clients can be updated with it. It’s like having your mail sent to an assistant at the post office who categorizes it and stores it for you, gives it to you whether you’re at home, at work, or actually there, and makes changes to the stored copies as you do.
You can keep a properly marked archive on your home client as well as on your mail server. IMAP also supports an offline mode; changes are synched with the server the next time you’re online. You can configure IMAP mail servers to fetch mail from POP inboxes, too, which works really well if you’re looking to consolidate. Of course, since IMAP works with the “cloud” ideal, server access and storage can be issues. Thankfully, the easiest way to avoid this is to simply move email from the INBOX to your local folder in your favorite email software. This can definitely be a trade-off for most people with todays mobile devises.